API STD 594 pdf download Check Valves: Flanged, Lug, Wafer, and Butt-welding 5.1.3 For Type “A” valves, the purchase order shall specify whether the body type shall be wafer, lug, or doubleflanged; for Type “B” valves, the purchase order shall specify whether the body type shall be flanged or butt-welding. 5.1.3.1 End and cover flanges shall be integrally cast or...